Histamine was first identified as a hormone (Barger, G. and H. H. Dale, J. Physiol. (London) 1910, 41:19-59) and has since been demonstrated to play a major role in a variety of physiological processes, including the inflammatory “triple response” via H1 receptors (Ash, A. S. F. and H. O. Schild, Br. J. Pharmac. Chemother. 1966, 27:427-439), gastric acid secretion via H2 receptors (Black, J. W. et al., Nature 1972, 236:385-390), and neurotransmitter release in the central nervous system via H3 receptors (Arrang, J.-M. et al., Nature 1983, 302:832-837) (for review see Hill, S. J. et al., Pharmacol. Rev. 1997, 49(3):253-278). All three histamine receptor subtypes have been demonstrated to be members of the superfamily of G protein-coupled receptors (Gantz. I. et al., Proc. Natl. Acad. Sci. U.S.A. 1991, 88:429-433; Lovenberg, T. W. et al., Mol. Pharmacol. 1999, 55(6):1101-1107; Yamashita, M. et al., Proc. Natl. Acad. Sci. U.S.A. 1991, 88:11515-11519). There are, however, additional functions of histamine that have been reported, for which no receptor has been identified. For example, in 1994, Raible et al. demonstrated that histamine and R-α-methylhistamine could activate calcium mobilization in human eosinophils (Raible, D. G. et al., Am. J. Respir. Crit. Care Med. 1994, 149:1506-1511). These responses were blocked by the H3-receptor antagonist thioperamide. However, R-α-methylhistamine was significantly less potent than histamine, which was not consistent with the involvement of known H3 receptor subtypes. Therefore, Raible et al. hypothesized the existence of a novel histamine receptor on eosinophils that was non-H1, non-H2, and non-H3. Most recently several groups (Oda, T. et al., J. Biol. Chem. 2000, 275(47):36781-36786; Liu, C. et al., Mol. Pharmacol. 2001, 59(3):420-426; Nguyen, T. et al., Mol. Pharmacol. 2001, 59(3):427-433; Zhu, Y. et al., Mol. Pharmacol. 2001, 59(3):434-441; Morse, K. L. et al., J. Pharmacol. Exp. Ther. 2001, 296(3):1058-1066) have identified and characterized a fourth histamine receptor subtype, the H4 receptor. This receptor is a 390 amino acid, seven-transmembrane, G protein-coupled receptor with approximately 40% homology to the histamine H3 receptor. In contrast to the H3 receptor, which is primarily located in the brain, the H4 receptor is expressed at greater levels in eosinophils and mast cells, among other cells, as reported by Liu et al. (infra) and Hofstra et al. (J. Pharmacol. Exp. Ther. 2003, 305(3):1212-1221). Because of its preferential expression on immunocompetent cells, this H4 receptor is closely related with the regulatory functions of histamine during the immune response.
A biological activity of histamine in the context of immunology and autoimmune diseases is closely related with the allergic response and its deleterious effects, such as inflammation. Events that elicit the inflammatory response include physical stimulation (including trauma), chemical stimulation, infection, and invasion by a foreign body. The inflammatory response is characterized by pain, increased temperature, redness, swelling, reduced function, or a combination of these.
Mast-cell de-granulation (exocytosis) releases histamine and leads to an inflammatory response that may be initially characterized by a histamine-modulated wheal and flare reaction. A wide variety of immunological stimuli (e.g., allergens or antibodies) and non-immunological (e.g:, chemical) stimuli may cause the activation, recruitment, and de-granulation of mast cells. Mast-cell activation initiates allergic (H1) inflammatory responses, which in turn cause the recruitment of other effector cells that further contribute to the inflammatory response. The histamine H2 receptors modulate gastric acid secretion, and the histamine H3 receptors affect neurotransmitter release in the central nervous system.
Modulation of H4 receptors controls the release of inflammatory mediators and inhibits leukocyte recruitment, thus providing the ability to prevent and/or treat H4-mediated diseases and conditions, including the deleterious effects of allergic responses such as inflammation. Compounds according to the present invention have H4 receptor modulating properties. Compounds according to the present invention have leukocyte recruitment inhibiting properties. Compounds according to the present invention have anti-inflammatory properties.
Examples of textbooks on the subject of inflammation include Gallin, J. I. and R. Snyderman, Inflammation: Basic Principles and Clinical Correlates, 3rd Edition, (Lippincott Williams & Wilkins, Philadelphia, 1999); V. Stvrtinova, V. et al., “Inflammation and Fever”, Pathophysiology Principles of Diseases (Textbook for Medical Students, Academic Press, 1995); Cecil et al., Textbook Of Medicine, 18th Edition (W.B. Saunders Company, 1988); and Steadmans Medical Dictionary.
Background and review material on inflammation and conditions related with inflammation can be found in articles such as the following: Nathan, C. Nature. 2002, 420:846-852; Tracey, K. J. Nature 2002, 420:853-859; Coussens, L. M. and Z. Werb, Nature 2002, 420:860-867; Libby, P. Nature 2002, 420:868-874; Benoist, C. and D. Mathis, Nature 2002, 420:875-878; Weiner, H. L. and D. J. Selkoe, Nature 2002, 420:879-884; Cohen, J. Nature 2002, 420:885-891; Steinberg, D. Nature Medicine 2002, 8(11):1211-1217.
Inflammation herein refers to the response that develops as a consequence of histamine release, which in turn is caused by at least one stimulus. Examples of such stimuli are immunological stimuli and non-immunological stimuli.
Inflammation is due to any one of a plurality of conditions such as allergy, asthma, chronic obstructed pulmonary disease (COPD), atherosclerosis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases (including Crohn's disease and ulcerative colitis), psoriasis, allergic rhinitis, scleroderma, autoimmune thyroid diseases, immune-mediated (also known as type 1) diabetes mellitus and lupus, which are characterized by excessive or prolonged inflammation at some stage of the disease. Other autoimmune diseases that lead to inflammation include Myasthenia gravis, autoimmune neuropathies, such as Guillain-Barré, autoimmune uveitis, autoimmune hemolytic anemia, pernicious anemia, autoimmune thrombocytopenia, temporal arteritis, anti-phospholipid syndrome, vasculitides, such as Wegener's granulomatosis, Behcet's disease, dermatitis herpetiformis, pemphigus vulgaris, vitiligio, primary biliary cirrhosis, autoimmune hepatitis, autoimmune oophoritis and orchitis, autoimmune disease of the adrenal gland, polymyositis, dermatomyositis, spondyloarthropathies, such as ankylosing spondylitis, and Sjogren's syndrome. Regarding the onset and evolution of inflammation, inflammatory diseases or inflammation-mediated diseases or conditions include, but are not limited to, acute inflammation, allergic inflammation, and chronic inflammation.
Cited references are incorporated herein by reference.